Road Design & Centripetal Force

Road designers must account for skid conditions by giving curved roads and curved access ramps a slight angle of inclination .  

This is done to minimize (or reduce to zero) the need for friction which is particularly important for high speed, high efficiency situations.  

In this situation the horizontal component of the normal force equal the centripetal force.  

The values of the angle of inclination, the radius of curvature of the banked road,  and the speed at which this condition is met are factors in what is known as the "design values" of the road. 

On highway ramps the maximum speed is determined by the design values.
The purpose of banking is to reduce skidding, and improve traction on curves and access ramps.

 banked road

A banked section of Highway #427 in Toronto  L. Lista 2001©

The forces acting on a vehicle on a banked road can be illustrated with te diagram below:

This is the equivalent free body diagram on a banked road

The Centripetal Force on a banked road can be simplified as such:

Note that the centripetal force is acting along the radius of curvature of the banked road which is horizontal.

It does not act along the incline - a common misconception. This is also the direction of the centripetal acceleration.